The Trump administration just issued a draft rule that would prevent illegal immigrants from claiming federal housing subsidies. The reform will help ensure that taxpayer dollars only go to needy American families. Though welcome and much needed, the rule doesn’t address the root of the problem — the widespread lack of affordable housing in this country. More than 10 million Americans depend on federal welfare programs to pay rent. Tens of millions more qualify for such assistance but don’t receive any help due to programs’ budget constraints. America’s immigration laws deserve part of the blame for this sorry state of...